Carbon nanotube composite and preparation method of the same

ABSTRACT

A carbon nanotube (CNT) composite of which one or more specific functional groups are bonded to surface of a CNT, and a method of preparing a CNT composite are provided. The method includes the steps of introducing an acylhalide group to surface of a CNT, and causing a reaction of the acylhalide group with a polysiloxane having amine groups so as to prepare a CNT composite of which the polysiloxane is bonded to the surface by the medium of an amide group. The CNT composite can fix metal particles uniformly and densely thereon, can have improved mechanical and electrical properties, and can be applied to various industrial fields.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to and the benefit of Korean PatentApplication No. 10-2009-0128444 filed in the Korean IntellectualProperty Office on Dec. 21, 2009, the entire contents of which areincorporated herein by reference.

BACKGROUND OF THE INVENTION

(a) Field of the Invention

The present invention relates to a carbon nanotube (CNT) composite and apreparation method of the same, and particularly to a CNT composite onwhich metal particles can be uniformly fixed, that has improvedmechanical and electrical properties, and that can be applied to variousindustrial fields, and a preparation method of the same.

(b) Description of the Related Art

Since the discovery of carbon nanotubes (CNT) was reported by Iijima in1991, numerous studies regarding CNT as a nano-material have beenundertaken, and remarkable improvements in the physical and mechanicalproperties of the CNT have been reported by many researchers.

Recently, interest in the CNT has increased because the CNT is expectedto contribute to future nano-engineering fields when it is used as areacting template for growing nanotubes or nanorods of other materials.Particularly, applied research on nano-electron device technologies suchas a CNT memory and a logic device that will overcome the limitations ofthe present semiconductor technology, a field emission emitter and adisplay application technology using its superior field emissionproperty, application technologies of a fuel cell and a lithium ionbattery using its large surface area, a composite for an electromagneticshield and a highly sensitive material, a highly sensitive nano-sensor,and the like are being carried out at home and abroad.

Furthermore, research on CNT-nanoparticle composites of which thenanoparticles are bonded to the CNT is actively being undertaken.According to the research, the CNT-nanoparticle composite can be appliedto a catalyst, a chemical sensor, or a nano-sized electromagneticdevice, because it is possible to apply the properties of thenanoparticles as well as the properties of the CNT itself. For suchapplications, various technologies for fixing the nanoparticles to theCNT while maintaining the inherent properties of the CNT and thenanoparticles are being developed.

Particularly, since the CNT-metal nanoparticle composite can be utilizedas many forms of electronic materials, various methods for fixing themetal nanoparticles to the CNT have been suggested. For example, apreparation method of the composite by physically mixing the CNT andmetals has been suggested, but it has a disadvantage in that it isdifficult to apply the composite as an electronic material, because themetals are not properly bonded to the CNT in the composite, or are notdispersed uniformly and are agglomerated together. Accordingly, a methodof chemically bonding the metal to the CNT has been suggested, but ithas a problem that the metal nanoparticles are not uniformly fixed tothe CNT and the size of the metal particles fixed thereto is notuniform.

SUMMARY OF THE INVENTION

An aspect of the present invention is to provide a CNT composite thatcan fix metal particles uniformly and highly densely on the surface ofCNT, has improved mechanical and electrical properties, and can beapplied to various industrial fields.

Another aspect of the present invention is to provide a preparationmethod of the CNT composite.

The present invention provides a CNT composite of which one or morespecific functional groups are bonded to surface of a CNT.

The present invention also provides a preparation method of the CNTcomposite including the steps of introducing an acylhalide group to thesurface of a CNT, and causing a reaction of the acylhalide group with apolysiloxane having amine groups so as to prepare a CNT composite ofwhich the polysiloxane is bonded to the surface by the medium of anamide group.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic process of the method of preparing the CNTcomposite to which metal particles are fixed.

FIG. 2 shows TEM photographs showing the CNT composite to which silvernanoparticles are fixed.

FIGS. 3 to 10 show TEM photographs showing the CNT composites ofComparative Examples 1 to 8 to which metal nanoparticles are fixed.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Hereinafter, a CNT composite and a preparation method of the sameaccording to the embodiments of the present invention are explained inmore detail.

According to one embodiment of the present invention, a CNT composite ofwhich one or more functional groups represented by the followingChemical Formula 1 are bonded to the surface of a CNT may be provided.

In Chemical formula 1, n may be an integer of 1 to 10, R₁ and R₆ mayindependently be hydrogen or a C₁-C₃ alkyl, and R₂, R₃, R₄, and R₅ mayindependently be a C₁-C₃ alkyl or phenyl.

Through experiments, the present inventors confirmed that metalnanoparticles can be uniformly and highly densely decorated on the CNT,which may be prepared by the method disclosed below, withoutagglomerating, and the CNT composite having metal nanoparticles can haveexcellent electrical conductivity, and completed the present invention.Such CNT composite may have a form in which one or more functionalgroups are introduced to the surface of the CNT, and the part derivedfrom the polysiloxane compound in Chemical Formula 1 acts to fix themetal nanoparticles uniformly. By applying the CNT composite, it ispossible to prepare electronic materials that have excellent mechanicaland electric properties, and the composite can be easily applied tovarious industrial fields. Particularly, the electronic materials towhich the CNT composite is applied can be applied to the fields ofisotropic conductive adhesives, solder joint technologies, and the likein the electronic package industry.

In Chemical Formula 1, the n may be an integer of 1 to 10, andpreferably an integer of 5 to 10. When the n is over 10, the functionalgroups of Chemical Formula 1 may be tangled, and thus it may bedifficult to fix the metal nanoparticles to the CNT composite.

The CNT can be obtained by a commonly known preparation method, and amethod using arc discharge, a method of using a laser, a method of usingcarbon monoxide (CO) in the condition of high temperature and highpressure, a thermal chemical vapor deposition synthesis method, and thelike can be exemplarily used. However, the CNT used in one embodiment ofthe present invention is not limited to what is prepared by the methods,and the CNT that is commonly used and obtained can be applied to thepresent invention without particular limitation.

Meanwhile, the CNT composite according to one embodiment of the presentinvention may further include a metal nanoparticle, and specificexamples of the metal nanoparticle may be nanoparticle of palladium(Pd), rhodium (Rh), iridium (Ir), platinum (Pt), gold (Au), silver (Ag),or a mixture thereof, and preferably silver nanoparticles.

Meanwhile, the metal nanoparticle may be fixed to the CNT compositethrough a coordination interaction by the medium of the functionalgroups of Chemical Formula 1. The functional groups of Chemical Formula1 may form particular sites on the CNT composite where the nanoparticlescan be fixed regularly and uniformly, and the metal nanoparticles may befixed to the composite through the coordination interaction by themedium of the functional groups. Thus, the metal nanoparticles may bebonded to the CNT composite with a uniform size and appropriatestrength.

Meanwhile, according to another embodiment of the present invention, amethod of preparing a CNT composite includes the steps of introducing anacylhalide group to the surface of CNT, and causing a reaction of theacylhalide group with a polysiloxane having amine groups so as toprepare a CNT composite of which the polysiloxane is bonded to thesurface of the CNT by the medium of an amide group.

Through experiments, the present inventors confirmed that the CNTcomposite, of which the polysiloxane is bonded to the surface of the CNTby the medium of an amide group, is prepared by introducing anacylhalide group to surface of a CNT and reacting the acylhalide groupwith a polysiloxane having amine groups. Moreover, it is also confirmedthat metal nanoparticles can be uniformly fixed to the CNT compositewithout agglomerating and the CNT composite having metal nanoparticlescan have excellent electrical conductivity. Particularly, it is alsorecognized by the experiments that metal nanoparticles can be fixed moreuniformly by applying a particular reaction condition during fixing ofthe metal nanoparticles to the CNT composite.

The step of introducing the acylhalide group may include the steps oftreating the CNT with an acid, and causing a reaction of theacid-treated CNT with a halogenating agent.

The CNT can be used without particular limitation if it can be preparedby commonly known methods, and examples of such methods are as disclosedabove. Furthermore, the acid treatment step of the CNT may be carriedout in a solution including sulfuric acid, hydrochloric acid, nitricacid, and the like. The kinds of the acid, the concentration of theacid, and the conditions such as the reaction time, the reactiontemperature, and the like are not particularly limited, and any commonlyknown method that can be applied to treat the CNT with an acid can beused without particular limitation.

Furthermore, thionyl chloride or phosphorus chloride, such as phosphorusdichloride, phosphorus trichloride, and phosphorus pentachloride, may beused as the halogenating agent.

Furthermore, the polysiloxane having amine groups may include thecompound of the following Chemical Formula 2.

In the Chemical Formula 2, n may be an integer of 1 to 10, R₁ and R₆ mayindependently be hydrogen or a C₁-C₃ alkyl, and R₂, R₃, R₄, and R₅ mayindependently be a C₁-C₃ alkyl or phenyl. And preferably, R₃ and R₄ mayindependently be methyl or phenyl.

Furthermore, the polysiloxane having amine groups may include apolydimethylsiloxane, a polydiphenylsiloxane, apolymethylphenylsiloxane, or a mixture thereof.

Meanwhile, in another embodiment of the present invention, the methodmay further include the step of dispersing the CNT composite withultrasonic waves in the presence of an organic solvent. Throughexperiments, it can be recognized that the CNT composites wereagglomerated or tangled before the ultrasonic dispersion in the organicsolvent, but the CNT composites were dispersed well after the ultrasonicdispersion. Therefore, the metal nanoparticles can be fixed moreuniformly because the CNT composites are dispersed well through theultrasonic dispersion process and the exposed surface area increases. Amethod and apparatus that are commonly used or known for dispersing andcleaning organic compounds can be used in the ultrasonic dispersion.Particularly, a commercial apparatus such as bar sonicator and the likecan be used, but it is not limited to this. Furthermore, tetrahydrofuran(THF) can be used as the organic solvent, but it is not limited to this,and any known solvent that is commonly used for dispersing and cleaningorganic compounds can be used without particular limitation.

Furthermore, another embodiment of the present invention may furtherinclude the step of curing the prepared CNT composite. Through thecuring step, particular sites where the metal nanoparticles can be fixedwith appropriate strength are formed on the CNT composite, and the metalnanoparticles can be fixed to the composite more easily and uniformlybecause the positions of the sites have uniform regularity and the sizeis also appropriately controlled.

The curing step may be carried out at a temperature of 260 to 300° C. Asshown in the example disclosed below, Comparative Examples 7 and 8, andFIGS. 9 and 10, when the curing temperature is lower than 260° C., themetal nanoparticles may not be fixed uniformly or may be agglomerated.Furthermore, when the curing temperature is higher than 300° C., theproperties of the final product, the CNT composite, such as theelectrical conductivity and the like, may be deteriorated.

Meanwhile, in another embodiment of the present invention, the methodmay further include the step of fixing a metal nanoparticle to the CNTcomposite. As disclosed above, the metal nanoparticle may include atleast one nanoparticle of palladium (Pd), rhodium (Rh), iridium (Ir),platinum (Pt), gold (Au), or silver (Ag), and preferably silvernanoparticles.

The step of fixing the metal nanoparticle to the CNT composite mayinclude the step of causing a reaction of the CNT composite in aprecursor solution of the metal nanoparticle. If the CNT compositereacts in the precursor solution of the metal nanoparticle, the metalnanoparticle can be uniformly fixed to the CNT composite withappropriate strength through the coordination interaction bonding.

The precursor solution of the metal nanoparticle may include a nitrate,a sulfate, a chloride salt of said metals, and a silver nitrate solutioncan preferably be used.

The precursor solution of the metal nanoparticle may have aconcentration of 0.1 to 0.5M. When the concentration is lower than 0.1M,the amount of the metal nanoparticle fixed to the surface of the CNTcomposite may be insufficient, and when the concentration is higher than0.5M, the metal nanoparticle may be agglomerated on the CNT composite ornot uniformly fixed, and the electrical conductivity of the compositemay deteriorate. Particularly, when the concentration is higher than0.5M, the metal nanoparticle cannot be uniformly fixed as shown inComparative Examples 3 and 4 disclosed below, and in FIGS. 5 and 6.

Furthermore, the step of fixing the metal nanoparticle may be carriedout at a temperature of 130 to 150° C. If the temperature in the step offixing the metal nanoparticle is too high or too low, the metalnanoparticle may be unevenly fixed to the composite, or the size of thefixed metal nanoparticles becomes irregular. Therefore, the electricalconductivity of the composite to which the metal nanoparticles are fixedat the temperature outside of the range may be largely deteriorated. Asshown in Comparative Examples 1 and 2 disclosed below, and FIGS. 3 and4, it can be recognized that the metal nanoparticle may not be fixeduniformly outside of the temperature of 130 to 150° C.

Furthermore, the step of fixing the metal nanoparticle may be carriedout for 30 to 90 minutes. When the step of fixing the metal nanoparticleis carried out for less than 30 minutes, the amount of the metalnanoparticle fixed to the CNT may be insufficient, and when the time isover 90 minutes, the metal nanoparticle may be agglomerated on the CNTcomposite and the electrical conductivity of the composite maydeteriorate.

According to the present invention, it is possible to fix the metalparticles uniformly, and it is also possible to provide the CNTcomposite that has improved mechanical and electrical properties and canbe applied to various industrial fields.

Hereinafter, functions and effects of the present invention areexplained in more detail through concrete examples of the invention.However, the examples are provided only for exemplifying the presentinvention, and the scope of the present invention is not determined toor by this.

EXAMPLE Preparation of the CNT to which the Metal Particle is Fixed

Acid Treatment on the CNT

The CNT (Hanwha Nanotech Co., Korea) was put in an 80° C. aqueous acidsolution and reacted for 2 hours, wherein the aqueous acid solution wasprepared by mixing sulfuric acid and nitric acid in a ratio of 3:1 andadding distilled water thereto so as to adjust the content of the acidto be 40%.

The acid-treated CNT was obtained by mixing the product of the abovereaction with excess distilled water, and eliminating the solutionincluding impurities by filtering the same. The processes of mixing withdistilled water and filtering were repeated until the pH of the aqueoussolution including the acid-treated CNT became about 7, and theacid-treated CNT was obtained by filtering the solution with a Teflonfilter (pore size: 0.2 μm) and drying the product.

Acylation of the Acid-Treated CNT

The acid-treated CNT and an excess of thionyl chloride were refluxed ina 65° C. oil-bath for 24 hours. Then, the product was washed 4 timeswith tetrahydrofuran (THF) and filtered with the Teflon filter (poresize: 0.2 μm). The filtered product was sufficiently dried in an 80° C.oven for 24 hours, and a halogen acylated CNT (CNT-CO-CI) powder wasobtained.

Preparation of the CNT Composite

The halogen acylated CNT (CNT-CO-CI) powder and polydimethylsiloxane(PDMS) having amine end groups (KF-8012, Shin-Etsu Chemical Co., Ltd.,JAPAN/the equivalent of functional group 2200) were dispersed withultrasonic waves in an ice bath by using a bar sonicator for 10 minutes.Then, the product of the ultrasonic dispersion was filtered, dispersedin THF solvent with ultrasonic waves for 2 minutes, and washed. Thewashed product was then filtered, dispersed in THF solvent withultrasonic waves for 2 minutes, and washed again.

After finishing the washing process with THF, the CNT composite wascured at the curing temperature of 270° C. for 1 hour. The surface stateof the CNT composite was observed by the FESEM and TEM photographs, andit was shown that the thickness of the polydimethylsiloxane having amineend groups was 1 to 5 nm.

Fixation of the metal particles to the CNT composite 0.4M of silvernitrate was mixed with N-methyl-2-pyrrolidone (NMP) and dispersed withultrasonic waves. The prepared CNT composite was put in said silvernitrate solution and dispersed with ultrasonic waves for 3 minutes, andthen the nano-sized silver particles were fixed to the surface of theCNT composite with a reaction temperature of 140° C. and a reaction timeof 1 hour.

After the reaction was finished, the CNT composite to which the silvernanoparticles were fixed was observed by using a TEM, and the resultsare shown in FIG. 2. Further, it is recognized in FIG. 2 that the silverparticles are uniformly and densely fixed to the surface of the CNTcomposite.

COMPARATIVE EXAMPLES Preparation of the CNT to which the Metal Particlesare Fixed Comparative Examples 1 to 8

In Comparative Examples 1 to 6, CNT composites to which the silverparticles were fixed were prepared substantially according to the samemethod as in the example, except that the reaction temperature, theconcentration of the silver nitrate, and the reaction time in the stepof fixing the metal nanoparticles to the CNT were applied as disclosedin the following Table 1, and the curing process was omitted in thebonding step of the acylated CNT and the polysiloxane having amine endgroups.

In Comparative Examples 7 and 8, the CNT composites to which the silverparticles were fixed were prepared substantially according to the samemethod as in the example, except that the reaction temperature, theconcentration of the silver nitrate, and the reaction time in the stepof fixing the metal nanoparticles to the CNT, and the curing temperaturein the bonding step of the acylated CNT and the polysiloxane havingamine end groups were applied as disclosed in the following Table 1.

TABLE 1 Reaction Conditions in Example and Comparative Examples 1 to 8Curing Reaction Silver Nitrate Temper- Temperature ConcentrationReaction ature (° C.) (M) Time (hr) (° C.) Example 140 0.4 1 270 Comp.Example 1 120 0.4 1 — Comp. Example 2 160 0.4 1 — Comp. Example 3 1400.6 1 — Comp. Example 4 140 0.8 1 — Comp. Example 5 140 0.4 2 — Comp.Example 6 140 0.4 3 — Comp. Example 7 140 0.4 1 230 Comp. Example 8 1400.4 1 250

The CNTs of Comparative Examples 1 to 8 to which metal particles werefixed were observed by a TEM, and the results are shown in FIGS. 3 to10. From these results, it is recognized that the metal nanoparticlesare fixed uniformly when the reaction temperature, the concentration ofthe silver nitrate, the reaction time in the step of fixing the metalnanoparticles to the CNT, the curing temperature in the bonding step ofthe acylated CNT, and the polysiloxane having amine end groups arecontrolled to be in a particular range.

Comparative Example 9

The metal nanoparticles were directly fixed to the acid-treated CNTsubstantially according to the same method as in the example, exceptthat the acylation step and the step of reacting the CNT and thepolydimethylsiloxane (PMDS) having amine end groups were omitted.

Experimental Examples Measurement of Electric Conductivity

The metal nanoparticles-CNT composites prepared in the example andComparative Example 9 were mixed with polydimethylsiloxane respectivelyaccording to the following Table 2, and coated on a polyethyleneterephthalate (PET) film with the thickness of 0.8 μm by using a barcoater.

Further, the electrical conductivities of the coating layers weremeasured by using a 4-probe method (Loresta-GP, Mitsubishi Chemical Co.,Japan).

TABLE 2 Results of the electrical conductivities Comparative Example(S/cm) Example 9 (S/cm) CNT 1 wt % 4.59 × 10⁻⁷ 1.94 × 10⁻⁷ CNT 2 wt %3.66 × 10⁻³ 3.75 × 10⁻⁵ CNT 3 wt % 7.84 × 10⁻² 1.01 × 10⁻³

As shown in Table 2, it is recognized that the example in which themetal nanoparticles are fixed to the CNT composite prepared by applyingthe polysiloxane having amine end groups shows higher electricalconductivity than Comparative Example 9 in which the metal nanoparticlesare fixed to the CNT that is only treated with an acid. It is alsorecognized that the increasing effect of the electrical conductivitybecomes larger as the concentration of the CNT increases.

Therefore, the CNT composite of the example enlarges the increasingeffect of the electrical conductivity, can have improved mechanical andelectrical properties, and can be applied to various industrial fields,because it fixes the metal nanoparticles uniformly.

1. A carbon nanotube (CNT) composite, of which one or more functionalgroups represented by the following Chemical Formula 1 are bonded to thesurface of a CNT:

wherein, in Chemical formula 1, n is an integer of 1 to 10, R₁ and R₆are independently hydrogen or a C₁-C₃ alkyl, and R₂, R₃, R₄, and R₅ areindependently a C₁-C₃ alkyl or phenyl.
 2. The CNT composite according toclaim 1, further comprising a metal nanoparticle.
 3. The CNT compositeaccording to claim 2, wherein the metal nanoparticle comprises at leastone metal nanoparticle selected from the group consisting of palladium(Pd), rhodium (Rh), iridium (Ir), platinum (Pt), gold (Au), and silver(Ag).
 4. The CNT composite according to claim 2, wherein the metalnanoparticle is bonded to the composite by the medium of the functionalgroup of Chemical Formula
 1. 5. A method of preparing a CNT composite,comprising the steps of: introducing an acylhalide group to surface of aCNT; and causing a reaction of the acylhalide group with a polysiloxanehaving amine groups so as to prepare the CNT composite of which thepolysiloxane is bonded to the surface of the CNT by the medium of anamide group.
 6. The method according to claim 5, wherein the step ofintroducing the acylhalide group comprises the steps of: treating theCNT with an acid; and causing a reaction of the acid-treated CNT with ahalogenating agent.
 7. The method according to claim 6, wherein thehalogenating agent comprises thionyl chloride or phosphorus chloride. 8.The method according to claim 5, wherein the polysiloxane having aminegroups comprises a compound of the following Chemical Formula 2:

wherein, in Chemical formula 2, n is an integer of 1 to 10, R₁ and R₆are independently hydrogen or a C₁-C₃ alkyl, and R₂, R₃, R₄, and R₅ areindependently a C₁-C₃ alkyl or phenyl.
 9. The method according to claim8, wherein R₃ and R₄ in Chemical Formula 2 are independently a methyl ora phenyl.
 10. The method according to claim 5, further comprising a stepof dispersing the CNT composite with ultrasonic waves in the presence ofan organic solvent.
 11. The method according to claim 5, furthercomprising a step of curing the CNT composite.
 12. The method accordingto claim 11, wherein the curing step is carried out at a temperature of260 to 300° C.
 13. The method according to claim 5, further comprising astep of fixing a metal nanoparticle to the CNT composite.
 14. The methodaccording to claim 13, wherein the step of fixing the metal nanoparticleto the CNT composite comprises the step of causing a reaction of the CNTcomposite in a precursor solution of the metal nanoparticles.
 15. Themethod according to claim 14, wherein the precursor solution of themetal nanoparticles has a concentration of 0.1 to 0.5M.
 16. The methodaccording to claim 13, wherein the step of fixing the metalnanoparticles to the CNT composite is carried out at a temperature of130 to 150° C. for 30 to 90 minutes.